Cochlear implant system component having multiple electrode assemblies

ABSTRACT

An electrode array ( 30 ) which is able to be inserted to a desired depth within the cochlea to provide useful percepts for the recipient which will also preferably not cause damage to the sensitive structures of the cochlea. The electrode array ( 30 ) is insertable through an opening in the cochlea and into at least the basal region of the cochlea and comprises an elongate carrier ( 31 ) having a proximal end, a distal end, and a plurality of electrodes ( 32 ) supported by the carrier at respective spaced locations thereon in a region between the proximal end and the distal end. A stabilizing collar ( 35 ) extends outwardly from the elongate carrier ( 31 ) at or adjacent a proximal end thereof and has an abutment surface adapted to abut a portion of the cochlea surface around the cochleostomy and at least substantially prevent movement of the carrier ( 31 ) following completion of insertion of the array ( 30 ) into the cochlea.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/518,811 entitled “Cochlear Implant Electrode Array” andfiled on Dec. 22, 2004. The entire disclosure and contents of the aboveapplication is hereby incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made partially with government support under GrantNo. DC000242-19 awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates to an implantable cochlear electrodeassembly. A method of implanting such a device is also described.

BACKGROUND OF THE INVENTION

In modern society, the occurrence of hearing loss is quite common, withapproximately 10% of the population suffering from some degree ofhearing impairment. This can be attributed to a number of causes, suchas prolonged exposure to loud sounds, the result of disease or illness,or congenital problems.

Hearing loss is generally of two types, namely conductive andsensorineural. Conductive hearing loss occurs when the normal mechanicalpathways for sound to reach the hair cells in the cochlea are impeded,for example, by damage to the ossicles. In such cases, the hearing lossmay often be improved by the use of conventional hearing aids, whichamplify the sound so that acoustic information reaches the cochlea andthe hair cells. Such hearing aids utilize acoustic mechanicalstimulation, whereby the sound is amplified according to a number ofvarying techniques, and delivered to the inner ear as mechanical energy.This may be through a column of air to the eardrum, or direct deliveryto the ossicles of the middle ear.

Sensorineural hearing loss, however, is due to the absence ordestruction of the hair cells in the cochlea which are needed totransduce acoustic signals into auditory nerve impulses. Individualssuffering from this type of hearing loss are unable to derive anybenefit from conventional hearing aid systems, no matter how loud theacoustic stimulus is made, because their mechanisms for transducingsound energy into auditory nerve impulses have been damaged. In suchcases, cochlear implants have been developed to provide the sensation ofhearing to such individuals. In cochlear implants, electricalstimulation is provided via stimulating electrodes positioned as closeas possible to the nerve endings of the auditory nerve, essentiallybypassing the role of the hair cells in a normally functioning cochlea.The application of a stimulation pattern to the nerve endings causesimpulses to be sent to the brain via the auditory nerve, resulting inthe brain perceiving the impulses as sound.

As has been alluded to above, the treatment of both of these types ofhearing loss has been quite different, relying on two quite differentprinciples to deliver sound signals to be perceived by the brain assound. It has been found that it is relatively common in hearingimpaired individuals to experience sensorineural hearing loss for soundsin the high frequency range, and yet still be able to discern sounds inthe middle to low frequency range, through the use of a conventionalhearing aid, or naturally. Traditionally, in the majority of such cases,the individual would only receive treatment to preserve and improve thehearing for the middle to low frequency sounds, most probably via aconventional hearing aid, and little would be done to attempt to restorethe hearing loss for the high frequency sounds. Only if the individuallost the ability to perceive the middle to low frequency sounds wouldconsideration then be given to restoring the hearing loss for the highfrequency sounds, in this case a cochlear implant would be considered apossible solution.

The specification for U.S. Pat. No. 6,231,604 introduces the concept ofcombining the two treatments, namely acoustic mechanical stimulation andelectrical stimulation, for individuals with some degree of intactresidual hearing. In this patent, the preferred embodiment makes mentionof acoustic mechanical stimulation being used for sounds representativeof low to mid-range frequencies in the acoustic environment, withelectrical stimulation being used for sounds representative of mid tohigh-range frequencies in the acoustic environment. Whilst this patentidentifies the need to attempt to combine the two stimulation methods itfails to suggest how such a system can be achieved, and the mechanismfor performing this task.

International patent publication WO 00/69513 describes a number ofembodiments of an electrode array that may be used to deliver electricalstimulation to the associated regions of the cochlea in order tosupplement hearing of high frequency sounds. In this publication, arelatively short and thin electrode array is described as being between6-8 mm in length and which is inserted through a small slit in the roundwindow membrane for stimulation of the basal end of the scala tympaniduct of the cochlea. In order to maintain the hydrodynamic nature of thecochlea, the described electrode array is provided with flexible flapsat its proximal end to assist in sealing the round window membrane andalso to maintain the array in a position that is remote from both wallsof the cochlea.

Experimental tests have shown that electrode arrays inserted to a depthas described by the above international patent publication will produceunnatural and sharp or high-pitched percepts in a recipient. Trials ofsuch an array to a depth of 8 mm into the cochlea have indicated thatrecipients are not able to fuse the electrical stimulus with theauditory stimulus received. Therefore, the electrode array as describedby the above-referenced patent publication will be unable to providebenefit to the recipient because of restriction in depth of insertionwhich is mandatory to preserve residual hearing. Further, the electrodearray of the above-referenced patent publication will most likely causedamage to the basal membrane due to rotation or twisting of the arrayabout its longitudinal axis. As the array relies upon flexible flaps forstabilization and not the fixation of the head of the device, it ishighly likely, due to the rounded shoulder of the device, that the arraywill not be stable within the cochlea, potentially causing damage to thesensitive structures therein. In addition, placement of such a devicethrough the round window membrane may interfere with the micromechanicsof the travelling wave of the inner ear.

The present invention is an attempt to address the perceived problems ofsuch prior art devices.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is solely forthe purpose of providing a context for the present invention. It is notto be taken as an admission that any or all of these matters form partof the prior art base or were common general knowledge in the fieldrelevant to the present invention as it existed before the priority dateof each claim of this application.

SUMMARY OF THE INVENTION

Throughout this specification the word “comprise”, or variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated element, integer or step, or group of elements, integers orsteps, but not the exclusion of any other element, integer or step, orgroup of elements, integers or steps.

The present invention aims to ameliorate the problems associated withthe prior art and provide an electrical stimulation device which is ableto restore high frequency sound perception whilst allowing naturalhearing mechanisms to be restored and maintained for perception of lowto medium frequency sounds.

The present invention also preferably aims to provide a stable and safeelectrode array which is able to be inserted to a desired depth withinthe cochlea to provide useful percepts for the recipient which will notcause damage to the sensitive structures of the cochlea.

The present invention also aims to provide a device which can be used toprovide electrical stimulation for high to medium frequency sounds andhas the ability, should a deterioration in the ability to perceivemedium to low sounds occur, to be easily adapted to apply electricalstimulation for a broad range of frequency sounds.

The present invention preferably provides a relatively very thin andshort electrode array that is insertable into the basal region of thecochlea and past the first turn thereof. The electrode array preferablyhas minimal impact on the hydrodynamic behaviour of the cochlea andallows the user to gain maximum benefit from any residual hearing thatthey may possess.

According to a first aspect, the present invention is an implantableelectrode array for insertion or which is insertable into at least thebasal region of the cochlea, the array comprising:

an elongate carrier having a proximal end, a distal end, and a pluralityof electrodes supported by the carrier at respective spaced locationsthereon in a region between the proximal end and the distal end; and

a stabilizing collar means extending outwardly from the elongate carrierat or adjacent a proximal end thereof, the stabilizing collar meanshaving an abutment surface adapted to abut at least a portion of thesurface of the cochlea and at least substantially prevent movement ofthe carrier following completion of insertion of the array into thecochlea.

In one embodiment, the array can be insertable through a cochleostomywith the collar means adapted to abut at least a portion of the cochleaaround the site of the cochleostomy.

In one embodiment of this aspect, the collar means can comprise aportion of the carrier having a diameter greater than that of theremainder of the carrier. The diameter of the collar means can beconstant along its length. In another embodiment, the diameter of thecollar means can vary along its length.

In one embodiment, the collar means can have a first portion in whichthe diameter of the collar means expands away from the proximal end ofthe collar means. In this embodiment, the diameter can expandfrusto-conically. The frusto-conical portion can comprise between about30% and 50% of the length of the collar means. The collar means canfurther comprise a second portion distal the proximal end of the collarmeans. The second portion is preferably constant in diameter along itslength. The second portion preferably comprises between about 70% and50% of the length of the collar means.

In one embodiment, the distal end of the collar means provides orcomprises the abutment surface. The abutment surface preferably extendsoutwardly from the carrier for a length. In a further embodiment, theabutment surface extends outwardly substantially at a right angle, morepreferably at a right angle, to the longitudinal axis of the carrier,when the carrier is straight. As such, the abutment preferably providesa corner in the outer surface of the carrier that is adapted to abut thesurface of the cochlea in the region around the site of insertion oncethe array has been inserted into place within the cochlea. This abutmentpreferably at least substantially prevents subsequent lateral movementof the array relative to the cochlea.

The collar means is preferably positioned at the proximal end of thecarrier. In a further embodiment, the collar means can be formedintegrally with the carrier member. For example, the collar means can bemoulded about the carrier member. In another embodiment, the collarmeans can be fabricated separately and connected to the carrier member.

In another embodiment, the stabilizing collar is made of a flexiblematerial at least similar to that used to form the carrier. Where thecarrier is fabricated from a silicone compound, the stabilizing collarmeans is also preferably fabricated from a silicone compound, includingthe same silicone compound or a different silicone compound.

In a further embodiment, the array can further comprise an anchoringmeans extending outwardly from the collar means. The anchoring means ispreferably adapted to be attached or anchored with body tissues and/orbone at or proximate the cochleostomy site. In one embodiment theanchoring means preferably extends outwardly at or adjacent the abutmentsurface of the collar means. In one embodiment, the anchoring means canbe made of a mesh material, such as Dacron. Sutures can preferably bepassed through the mesh material and into the tissue and/or bone tosecure the mesh to the tissue and/or bone. In one embodiment, theanchoring means is adapted to be sutured to the promontory bone.

In one embodiment, the mesh material comprising the anchoring means ismoulded at least partially within the collar means. The mesh ispreferably moulded at or adjacent the distal end of the collar means.The mesh preferably extends for a diameter that is at least about twicethe diameter of the collar means. Other diameters of the mesh can beenvisaged.

In one embodiment of this aspect, the array is preferably insertablewithin a cochlea to a depth that is at or beyond the first basal turn ofthe cochlea. In one embodiment, the array is insertable just beyond thefirst basal turn of the cochlea.

According to a second aspect, the present invention is an implantableelectrode array for insertion into at least the basal region of thecochlea, the array comprising:

an elongate carrier having a proximal end, a distal end, and a pluralityof electrodes supported by the carrier at respective spaced locationsthereon in a region between the proximal end and the distal end; and

an anchoring means extending outwardly from the elongate carrier at oradjacent a proximal end thereof and adapted to be anchored to bodytissues or bone surrounding the site of insertion and at leastsubstantially prevent movement of the carrier following completion ofinsertion of the array into the cochlea.

In one embodiment of this aspect, the array can be insertable through acochleostomy.

In this aspect, the anchoring means can be made of a mesh material, suchas Dacron. Sutures can preferably be passed through the mesh materialand into the tissue and/or bone to secure the mesh to the tissue and/orbone. In one embodiment of this aspect, the anchoring means is adaptedto be sutured to the promontory bone.

In a further embodiment of this aspect, the mesh material comprising theanchoring means is moulded into place within the body of the carrier.The mesh is preferably moulded at or adjacent a proximal end of thecarrier. The mesh preferably extends for a diameter that is at leastabout three times the diameter of the carrier. Other diameters of themesh can be envisaged.

In one embodiment of this aspect, the array is preferably insertablewithin a cochlea to a depth that is at or beyond the first basal turn ofthe cochlea. In one embodiment, the array is insertable just beyond thefirst basal turn of the cochlea.

In one embodiment of both of the above aspects, the carrier can adopt afirst configuration selected to allow the array to be inserted into arecipient's cochlea and at least a second configuration wherein saidelectrode array is adapted to apply tissue stimulation. The carrier ispreferably formed to preferentially adopt the second configuration oranother configuration different to said first configuration. The firstconfiguration of the carrier can be substantially straight or exactlystraight. In another embodiment, the first configuration can have adegree of curvature. In this embodiment, a distal portion of the carriercan have a degree of curvature. In this case, the distal portion cancomprise less than about 20% of the length of the carrier.

In a further embodiment of both aspects, the elongate carrier preferablyhas a length of between 8-12 mm. As described, the length can be suchthat the carrier is insertable to a depth that just extends beyond thefirst turn of the cochlea from the cochleostomy.

In a still further embodiment of both aspects, at least one of theelectrodes has a surface that is at least adjacent an inner surface ofthe carrier. More preferably, each of the electrodes in the array have asurface that is adjacent the inner surface of the carrier. In a furtherembodiment, the surfaces of the electrodes are aligned with the innersurface of the carrier. In another embodiment, the surfaces of theelectrodes stand proud of the inner surface of the carrier. It is alsoenvisaged that the electrode surface could also be recessed into theinner surface of the carrier. In yet another embodiment, one or moreelectrodes may also be positioned on the outer surface of the carriernot facing the modiolus. Such electrodes could act as additional groundor reference electrodes.

In yet another embodiment of both aspects, an indicator means may alsobe incorporated in the collar of the elongate carrier or at anotherlocation on the carrier to convey to the surgeon the orientation of theelectrodes on the array. It is envisaged that the indicator means couldbe any means capable of representing an orientation of the array wherebythe electrodes can be positioned as desired within the cochlea. In orderto achieve this, the indicator means is preferably provided on the partof the array which is adapted to be positioned external to the cochleafollowing implantation of the carrier.

According to a third aspect, the present invention is a method ofinserting an electrode array into at least the basal region of the scalatympani duct of a cochlea, said electrode array having a collar meansattached thereto at or adjacent a proximal end thereof, the methodcomprising the steps of:

(i) forming an opening into the cochlea to allow access to the scalatympani duct;

(ii) inserting a distal end of said electrode array into the scalatympani duct and advancing the array therein; and

(iii) at least abutting said collar means to the tissue surrounding saidopening in the cochlea, wherein said collar at least partially sealssaid opening into the cochlea and is arranged so that the electrodearray is stabilized within the cochlea.

In this aspect, the electrode array and collar means can have thefeatures of the array and collar means as defined herein.

In a further embodiment of this aspect, the method can comprise anadditional step prior to step (ii), in which a facia washer isfabricated and placed over said electrode array prior to its insertioninto the cochlea. The facia washer can comprise a piece of temporalisfascia that is harvested from the recipient. The facia washer can havedimensions of 3 mm×3 mm. Once harvested, the washer can be pressed in afascia press, before a sharp round instrument, such as a straight pick,is used to create a hole (eg. 0.4 mm in size) in the central portion ofthe stamp-like piece of fascia. The tip of the electrode is then passedthrough the hole until the fascia abuts the dacron mesh. The electrodeis then placed into the cochleostomy. The fascia washer assists insealing the inner ear from the middle ear.

In this aspect, the array can further comprise an anchoring meansextending outwardly from the collar means and wherein the methodcomprises an additional step of attaching said anchoring means to thetissue and/or bone at or proximate the site of insertion. In oneembodiment, the anchoring means can be sutured to the tissue and/orbone.

According to a fourth aspect, the present invention is a method ofinserting a cochlear electrode array into at least the basal end of thescala tympani duct of a cochlea, said cochlear electrode array having ananchoring means extending outwardly therefrom at or adjacent a proximalend thereof, the method comprising the steps of:

(i) forming an opening into the cochlea to allow access thereto;

(ii) inserting a distal end of said electrode array into the scalatympani duct and advancing the array therein; and

(iii) suturing said anchoring means to the tissue and/or bonesurrounding said opening in the cochlea so as to stabilize the arraywithin the cochlea.

In this aspect, electrode array and anchoring means can have thefeatures of the array and anchoring means as defined herein.

In both the third and fourth aspects, the step of forming an opening tothe cochlea can be performed via a normal cochleostomy using either a“soft surgery” technique with a diamond drill or laser to create a (eg.0.5 mm) cochleostomy anterior and caudal to the round window.

In the third and fourth aspects, the electrode array is preferablyformed with at least some degree of curvature and can be inserted intothe cochlea in a straight configuration, using a straightening stylet orwith a degree of curvature less than it normally adopts in a relaxedcondition. Following insertion to a depth of preferably about 10-12 mm,the straightening stylet is preferably removed and the array is allowedto return to its relaxed curved configuration. In this embodiment, adistal portion of the carrier can have a degree of curvature when thecarrier is in its relaxed condition. In this case, the distal portioncan comprise less than about 20% of the length of the carrier.

Following insertion, the electrode array would be positioned in a mannerwhereby the electrodes are able to apply stimulation to the appropriateregions of the cochlea that detect sounds having high frequencies. Theremaining structure of the cochlea would remain intact and allow therecipient to continue to use their residual hearing capability to detectsounds associated with middle to low frequency ranges.

In a further aspect, the present invention is an implantable componentof a cochlear implant system, the implantable component comprising:

a housing for a stimulator unit, the stimulator unit being adapted tooutput one or more stimulation signals;

a first elongate electrode assembly selectively activatable to applyelectrical stimulation in accordance with the output of the stimulatorunit; and

a second elongate electrode assembly selectively activatable to applyelectrical stimulation in accordance with the output of the stimulatorunit;

wherein only one of said first and second electrode assemblies isinsertable into the cochlea at any particular time.

In this aspect, the first elongate electrode assembly preferably hasless electrodes than said second electrode assembly and is adapted, wheninserted in the cochlea, to apply stimulation to the basilar region ofthe scala tympani of the cochlea. In one embodiment, the first electrodeassembly can have six electrodes. In another embodiment of this aspect,the first electrode assembly can comprise the implantable electrodearray according to the first or second aspects of the present invention.

In this aspect, the second electrode assembly is adapted, when insertedin the cochlea, to apply stimulation to the basilar region of the scalatympani and also to the region beyond the first basal turn. In oneembodiment, the second electrode assembly can comprise an electrodeassembly having 22 or 30 electrodes as is known in the art.

In this aspect, while the first electrode assembly is inserted in thecochlea, the second electrode assembly is preferably positioned externalto the cochlea and is inoperative. While the second electrode assemblyis inoperative, it is preferably coiled in the mastoid or is stored in abiocompatible package, such as a Teflon sack. While the second electrodeassembly is inserted in the cochlea, the first electrode assembly ispreferably positioned external to the cochlea and is inoperative.

The second electrode assembly may never be required but is implanted andis ready, in a subsequent surgery, to be inserted into the cochlea andrendered operable, if the recipient's hearing has deteriorated to theextent that they also no longer, at least readily, perceive middle tolow frequencies.

According to yet another aspect, the present invention is a method ofoperating a cochlear implant system, said system comprising:

a housing for a stimulator unit, the stimulator unit being adapted tooutput one or more stimulation signals; and

an elongate electrode assembly adapted to apply electrical stimulationto the cochlea of a recipient of the system in accordance with theoutput of the stimulator unit, the assembly having a proximal end and adistal end and comprising a plurality of electrodes disposed along itslength between the proximal end and the distal end, one or more of theelectrodes relatively closer to the proximal end being adapted toprovide stimulation to the basilar region of the cochlea and one or moreof the electrodes relatively closer to the distal end being adapted toprovide stimulation to a location beyond the first basal turn of thecochlea;

the method comprising the steps of:

while ever the recipient is only unable to hear relatively highfrequency sounds, only activating those one or more electrodes adaptedto provide stimulation to the basilar region of the cochlea.

In this aspect, the elongate electrode assembly is preferably relativelythin so as to at least substantially maintain the hydrodynamic nature ofthe cochlea.

In this aspect, those electrodes relatively closer to the distal end ofthe assembly are preferably able to be selectively made activatable asthe recipient's ability to perceive relatively lower frequenciesdeteriorates. In this regard, only six or some other number ofelectrodes may initially be operative and adapted to deliver stimulationto the basilar region of the cochlea. As the recipient's ability toperceive middle to low frequencies deteriorates, additional electrodesthat are positioned more deeply into the cochlea can be activated andbecome capable of delivering electrical stimulation. For example, anadditional three electrodes may be rendered capable of deliveringstimulation, then a farther three at a later time and so on until suchtime as all electrodes on the array are capable of deliveringstimulation. It will be appreciated that an additional three electrodesis only provided as an example and that more or less additionalelectrodes may be rendered operative as required to meet the particularrequirements of the recipient.

Activation of additional electrodes so as to render them capable ofdelivering electrical stimulation will preferably not require additionalsurgery. Rather, an external controller, as described below, will beused to modify the operation of the implantable component as required.

In all of the aspects, the electrode assembly preferably comprises acarrier member having a leading end that is insertable into a cochlea ofa recipient and a trailing end distal the leading end. The elongatecarrier member preferably has a plurality of electrodes mounted thereon.In one embodiment, the electrodes are mounted in a longitudinal array.Each of the electrodes have at least one wire, and possibly at leasttwo, extending from each electrode back towards the trailing end of thecarrier member.

The wires preferably extend back to the housing to at least a firstfeedthrough in the wall of the housing of the stimulator unit. In oneembodiment, the feedthrough provides hermetic and insulated electricalconnection for each wire extending from the electrode assembly into thehousing of the implantable component. Each feedthrough can be formedusing the method described in U.S. Pat. No. 5,046,242, the contents ofwhich are incorporated herein by reference. The electrodes arepreferably formed from a biocompatible electrically conducting material,such as a suitable metal, such as platinum.

The elongate carrier member is preferably formed from a resilientlyflexible material. In one embodiment, the carrier member can bepreformed from a plastics material with memory.

In a preferred embodiment, the elongate carrier member is formed from asuitable biocompatible material. In one embodiment, the biocompatiblematerial can be a silicone, such as a flexible siliconeelastomer-Silastic. Silastic MDX 4-4210 is an example of one suitablesilicone for use in the formation of the elongate member. In anotherembodiment, the elongate carrier member can be formed from apolyurethane or similar material.

In a preferred embodiment of the aspects, the implantable component canfurther comprise an additional electrode assembly that is adapted to beimplantable external of the internal passages of the cochlea. Thisadditional extracochlear electrode assembly is typically implantedexternal of the cochlea in the muscle surrounding the head of the user.The use of this additional assembly allows the stimulation method knownas monopolar stimulation to be performed. In monopolar stimulation, thestimulation passes between an intracochlear and an extracochlearelectrode, providing for a relatively wide current spread.

In a further embodiment, the housing for the stimulator used inconjunction with the electrode array is preferably implantable in arecess of the temporal bone adjacent the ear of the recipient that isreceiving the output of the implant system. The housing is preferablyformed from a biocompatible material or has a biocompatible coating. Thehousing can be coated with a layer of silicone or parylene.

The system preferably relies upon a receiver antenna to receive radiofrequency (RF) signals. The receiver antenna preferably comprises a wireantenna coil. The antenna coil can be comprised of at least one, andpreferably at least three, turns of electrically insulated platinum orgold wire tuned to parallel resonance by a capacitor internal to thehousing. The electrical insulation of the receiver antenna can beprovided by a thin, flexible silicone moulding and/or silicone orpolyurethane tubing.

The receiver antenna is preferably external of the housing of thestimulator unit. The moulding of the receiver antenna can also extendaround at least some of the housing of the stimulator unit. Electricalconnection between the antenna and componentry of the implantablecomponentry within the housing can be provided by two hermetic andelectrically insulated ceramic feedthroughs or an electrical conductor.The ceramic feedthroughs can be formed using the method described inabovementioned U.S. Pat. No. 5,046,242.

The receiver antenna of the implantable component preferably acts aspart of a radio frequency (RF) link to allow transcutaneousbidirectional data transfer between the implantable component and anexternal component of the system. The link preferably further comprisesan external antenna that is able to be aligned with the position of theimplantable receiver antenna. The radio frequency signals can bemodified to encode data using the method described in U.S. Pat. No.5,741,314. While described as a receiver antenna, the receiver antennacan preferably also transmit signals back to the transmitter antennawhich receives the signals for the purpose of telemetry from theimplanted component.

The link between the two antennae also provides a means of powering thecomponentry of the internal component. In the case where the implantablecomponent further has an on-board or implantable power source, such as arechargeable battery, the link can provide a means of inductivelycharging the battery when required.

When implanted, the housing preferably contains, in addition to thestimulator unit, a receiver unit. The receiver unit is preferablyadapted to receive signals from an external component that comprises atleast a controller. The controller is, in use, preferably mountedexternal to the body of the recipient such that the signals aretransmitted transcutaneously through the skin of the recipient.

The external controller can have a housing for a speech processoradapted to receive signals output by a microphone. During use, themicrophone can be mounted in the housing that is preferably supported onthe pinna of the recipient. Other suitable locations for the microphoneand/or the housing can be envisaged, such as a lapel of the recipient'sclothing.

The speech processor encodes the sound detected by the microphone into asequence of electrical stimuli following given algorithms, such asalgorithms already developed for cochlear implant systems. The encodedsequence is transferred to the implanted receiver/stimulator unit usingthe transmitter and receiver antennae. The implanted receiver/stimulatorunit demodulates the modulated signal and allocates the electricalpulses to the appropriate attached electrode by an algorithm which isconsistent with the chosen speech coding strategy. Allocation is alsoconsistent with the number of electrodes present in the array and/or thenumber of electrodes of the array that are in fact operative at thattime.

The external controller preferably further comprises a power supply. Thepower supply can comprise one or more rechargeable batteries. Thetransmitter and receiver antennae are used to provide power viatranscutaneous induction to the implanted receiver/stimulator unit andthe electrode array.

In a further embodiment, the receiver coil can be disposed about amagnet. The magnet, when present, is preferably centrally disposed inthe receiver coil. When present, the magnet can be used to hold andalign an external coil mounted to the outside of the head of therecipient. To achieve, this a ferromagnetic material or another magnetarranged to experience an attraction force to the magnet within thereceiver coil can be positioned in a central location within theexternal coil.

In one embodiment, the magnet can be removable from its location withinthe receiver coil.

While the implant system can rely on external componentry, in anotherembodiment, the controller, including the microphone, speech processorand power supply can also be implantable. In this embodiment, thecontroller can be contained within a hermetically sealed housing or thehousing used for the stimulator unit.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, a preferred embodiment of the invention is nowdescribed with reference to the accompanying drawings, in which:

FIG. 1 is a pictorial representation of a prior art cochlear implantsystem;

FIG. 2 a is a side view of an electrode array made in accordance withthe present invention;

FIG. 2 b is a medial side view of the electrode array of FIG. 2 a;

FIG. 3 is a simplified depiction of a cochlea representing issuesassociated with inserting shortened electrodes into the basal region ofthe cochlea;

FIG. 4 is a view of an electrode of the present invention in its relaxedstate;

FIG. 5 is a further simplified depiction of a cochlea representingfurther issues associated with inserting shortened electrodes into thebasal region of the cochlea; and

FIG. 6 shows an implantable device of a further embodiment of thepresent invention.

PREFERRED MODE OF CARRYING OUT THE INVENTION

Before describing the features of the present invention, it isappropriate to briefly describe the construction of one type of knowncochlear implant system with reference to FIG. 1.

Known cochlear implants typically consist of two main components, anexternal component including a speech processor 29, and an internalcomponent including an implanted receiver and stimulator unit 22. Theexternal component includes a microphone 27. The speech processor 29 is,in this illustration, constructed and arranged so that it can fit behindthe outer ear 11. Alternative versions may be worn on the body. Attachedto the speech processor 29 is a transmitter coil 24 that transmitselectrical signals to the implanted unit 22 via a radio frequency (RF)link.

The implanted component includes a receiver coil 23 for receiving powerand data from the transmitter coil 24. A cable 21 extends from theimplanted receiver and stimulator unit 22 to the cochlea 12 andterminates in an electrode array 20. The signals thus received areapplied by the array 20 to the basilar membrane 8 and the nerve cellswithin the cochlea 12 thereby stimulating the auditory nerve 9. Theoperation of such a device is described, for example, in U.S. Pat. No.4,532,930.

One embodiment of a cochlear implant electrode array, according to thepresent invention, is depicted generally as 30 in FIGS. 2 a and 2 b.FIG. 2 a is the side view of the electrode array 30 and FIG. 2 b is aview of the medial side of the electrode array 30. It can be consideredthat the medial side of the electrode array 30 is the side on which aplurality of spaced apart electrode contacts 32 are located.

As seen in FIGS. 2 a and 2 b, the electrode array 30 includes aplurality of spaced apart electrode contacts 32 on a flexible carrier31. In a preferred embodiment, each of the electrode contacts 32 resideon the same side, the medial side 33, of the carrier 31. Each electrodecontact 32 has at least one wire conductor 34 connected thereto. Thesewire conductors 34 are embedded within the flexible carrier 31 and exitthrough a proximal end of the carrier 31 within a flexible cable 21. Aspreviously described the flexible cable 21, including the wireconductors 34, is connected to the implanted receiver and stimulatorunit 22. The wires therefore provide the means for making electricalcontact with each of the electrode contacts 32 from unit 22.

At the proximal end of the electrode array 30 is a collar 35. The collar35 is larger in diameter than the carrier 31, and is made from a similarflexible material, such as silicone. The distal end of the collar 35provides an abutment surface 37. Embedded within the collar 35 adjacentthe surface 37 is an anchoring mesh material 6. In the depictedembodiment, the mesh material 36 is Dacron.

The right angle of the abutment surface 37 of the collar 35 with theouter surface of the carrier provides a square shoulder that at leastsubstantially prevents the array 30 from twisting following insertion inthe duct of a cochlea. The purpose of the mesh material 36 incorporatedinto and extending further outwardly that the collar 35 is to allow theface 41 of the mesh to be fixed and anchored to the promontory bone andintegrated into the surrounding fibrous tissue. This collar 35 andanchoring mesh 36 combination overcomes the problems associated withmovement of the short electrode over time, and prevents furtherpenetration of the electrode array 30 into the cochlea, as well as aidsgreatly in sealing the cochleostomy.

The wire conductors 34 pass through the collar portion 35, exiting viathe cable 21, which is connected to the collar portion 35 at itsproximal end.

The electrode array 30 also includes an indicator means 38 incorporatedinto the collar 35 to assist the surgeon in determining the orientationof the electrodes 32, once inserted into the cochlea. As the portion ofthe array, shown generally as 39, is intended to be inserted into thecochlea with only the mesh material 36 and the collar 35 being externalof the cochlea, it is important that the surgeon is provided with anindication as to the orientation of the surface of the array bearing theelectrodes 32. In one embodiment, the indicator means could be a portionof Dacron mesh correctly positioned on the collar 35 via a fasteningmeans such as glue, and covered with a clear silicone material,preferably the same material as that used to make the collar portion 35,to reform the tubular shape of the collar 35.

Alternatively, as opposed to the indicator means 38 being incorporatedinto the collar 35 as discussed above, the indicator means 38 can formpart of the collar 35, such as include a silicone marking on the collarportion 35, or be in the form of a notch or other similar marking on thecollar 35 or the mesh 36.

As shown in FIGS. 2 a and 2 b, the electrode contacts 32 are positionedon the medial side of the electrode array, ie. positioned on the sameside of the carrier 31. The array is preferably cylindrical and has asmall diameter resulting in the volume of the array 30 being minimized.Preferably, the cross sectional area of the array is 0.2×0.4 mm. Innormal hearing, the oscillation of the basilar membrane is required andthe amplitude of the sound is dependant on the damping of the membranemotion by the fluid within the cochlea. Therefore, it is important thatwhen an electrode array is inserted into the cochlea with the intentionto preserve this natural capacity to detect sounds, as is the case withthe present invention, the volume of the array must be minimized so thatthis damping will not be affected by the exclusion of the cochlea fluid.The electrode array 30 is of a smaller diameter than a conventionalelectrode array, and in the embodiment as shown, includes only 6electrodes 32.

It is envisaged that whilst the overall shape of the electrode array isdesigned to be thin to reduce the volume of the electrode array, it isconsidered that the cross-section of the array could have a variety ofshapes. In this regard, it is considered that the array could be round,oval, rounded square, hexagonal or octagonal and still fall within thespirit of the present invention.

Further, whilst the profile of the electrode array is shown as having asubstantially constant diameter along its length of between 0.1 and 0.4mm, it is also envisaged that the electrode array could have a taperedprofile from 0.4 mm at its end joining the collar 35 to 0.1 mm at thetip, or any variation in between.

The length of the inserted portion of the array L is preferably set tobe between 8-15 mm, more preferably between 9-12 mm. However it isenvisaged that in one embodiment of the present invention, the electrodearray could be as long as 20 mm as will be discussed in more detailbelow.

In a preferred embodiment, the array 30 is constructed, such as bymoulding, to have a slightly curved configuration when in its relaxedstate, as is shown in FIG. 4. A stylet (not shown for clarity) can beused to hold the array in a straight (or at least substantiallystraight) configuration for insertion. The use of a straightening styletis well known in the art and is discussed in detail in InternationalPublication No WO 00/71063, the contents of which are incorporatedherein by reference.

FIG. 3 is a simplified view of a cochlea 12 showing issues associatedwith inserting short electrodes into the cochlea. It has been foundexperimentally that an electrode inserted to a depth that is betweenpositions A & B will produce unnatural and sharp high pitch percepts fora recipient. In trials by the present applicant of a 6-electrode arrayinserted to a depth of 8 mm into the cochlea, it was found thatrecipients could not fuse the electrical stimulus with the auditorystimulus received. As a result, in such a device as described inInternational Publication No WO 00/69513, it is highly unlikely thatsuch an electrode would provide benefit to the user. Therefore, in orderto provide useful percepts to the recipient, the electrode array needsto be inserted beyond a depth of 6-8 mm. Providing this additional depthis, however, a challenge without damaging the osseous spinal lamina andbasilar membrane.

As described previously, for devices such as the present invention, itis essential that the hydrodynamic nature of the cochlea be preserved inorder to preserve the recipient's residual hearing. In order to achievethis it is essential that the sensitive structures of the cochlea bemaintained and that the array does not damage the walls of the cochleato alter the motion of the cochlea fluid. If the array is to be insertedbeyond position A depicted in FIG. 3, and to the desired depth toprovide useful benefit to the recipient, the array must be preventedfrom contacting the rear wall of the cochlea, shown as position B inFIG. 3. Therefore, in order to achieve this additional depth withoutcausing damage to the structure of the cochlea, the array is shaped withat least some degree of curvature to extend past the first turn of thecochlea, as shown as C in FIG. 3.

FIG. 4 shows the device of the present invention that is capable ofachieving the required depth of insertion. As shown, the array 30 is ofa curved configuration with each of the electrode contacts 32 positionedon the same side of the carrier for stimulation of the desired regionsof the cochlea. The array can be inserted into the cochlea in a straightconfiguration with the use of a straightening stylet (not shown)inserted into a lumen in the carrier 31. Upon insertion, the stylet canbe removed allowing the array 30 to assume its natural pre-curved shape.In this regard, the electrode array is able to settle close to themodiolus under the osseous spinal lamina to minimize impact on thehydrodynamic nature of the cochlea. It is envisaged that the array couldalso have the electrode contacts 32 positioned on diametrically opposedsurfaces of the carrier 31, rather than on the same surface and stillfall within the scope of the present invention. It is also envisagedthat instead of a straightening stylet being used to maintain the arrayin a straight position, a bioresorbable stiffening sheath could also beemployed to maintain the array in a straight position, with the sheathbeing dissolvable upon contact with cochlear fluid or saline solutionallowing the array to return to its pre-curved position.

FIG. 5 shows a further problem associated with prior art devicespostulated to perform the task of the present invention. One of themajor problems with prior art devices intended for insertion into thebasal section of the cochlea resides in the stability of the electrode.The fixation of the proximal end of the electrode is essential inproviding the desired stability of the electrode and to ensure that theelectrode will not move or twist and damage the basilar membrane andsensitive structures of the cochlea, thereby affecting the hydrodynamicnature of the cochlea. As is shown in FIG. 5, the cochlea is representeddiagrammatically as reference numeral 40, with the prior art array beingdepicted as the shaded region shown by reference numeral 45. Duringnatural body motion, unless the proximal end 42 of the electrode arrayis properly fixed, an electrode inserted this depth into the electrodewill experience a certain degree of rotation or twisting about the axisX-X, causing the electrode to damage the basilar membrane and affect theability of the cochlea to naturally detect sounds. This is particularlythe case where the proximal end of the device is rounded or relies uponflexible flaps or the like to maintain the array in the desiredposition.

With regard to the electrode array of the present invention as shown inFIG. 2 a, FIG. 2 b and FIG. 4, the stability of the electrode is ensuredthrough the design of the proximal end of the array. In this design theelectrode array is provided with a collar 35 having an abutment surface37 to stabilize the electrode and reduce any rotation of the deviceduring natural body movement. Further to this, the collar 35 has a meshportion 36 extending outwardly therefrom that allows the surgeon toanchor the collar to the promontory bone for integration into thefibrous tissue and additional stabilization. It is considered that theaction of this collar provides the desired stability to the device toenable the array to perform its desired function.

The electrode array of the present invention is preferably inserted intothe cochlea in the following manner. As the intention of the presentinvention is to preserve as much of the recipient's residual hearing aspossible so that only high frequency sounds are provided electrically,it is desirable that the structure of the cochlea is left intact as muchas possible. Therefore, rather than incising the round window membrane,a cochleostomy is formed. The cochleostomy is preferably made 1 mmanteroinferior to the round window and is preferably achieved usingeither a “soft surgery” technique or by drilling with a diamond burr orlaser. The electrode array is then inserted into at least the basalregion of the cochlea and secured in place as mentioned above. Prior toclosing the cochleostomy, tissue or muscle is packed behind the mesh tocreate a fascia washer. The fascia washer assists in sealing thecochleostomy and ensuring that the hydrodynamic nature of the cochlea ismaintained.

The electrode array is preferably made using conventional techniques,from conventional materials, as is known in the cochlear electrode arrayart. One approach for making a cochlear electrode array according to thepresent invention is described in International Publication No WO00/71063, the contents of which are incorporated herein by reference.

Turning to FIG. 6, there is shown the device of the present inventionaccording to a further embodiment. In this embodiment, the device isshown generally as 50, and represents the implantable portion of thesystem. With reference to FIG. 6 the receiver coil 23 is shown as wellas the receiver stimulator unit 22. Extending from the receiverstimulator unit 22 are three electrode arrays 51, 52, 53. Array 51corresponds with the short electrode array having a collar as describedabove, which is inserted into the basilar region of the cochlea toprovide electrical stimulation for high frequency sounds in accordancewith the first embodiment of the present invention. Array 52 isessentially a conventional electrode array consisting of a plurality ofelectrodes arranged along the length thereof to provide electricalstimulation for sounds of all frequencies as is the case forconventional cochlear implant devices. Array 52 can be placed into thecochlea if further hearing loss occurs in the future. Array 53 is anextra cochlear electrode as is known in conventional cochlear implantswhich is positioned remote from the cochlea to provide a reference pointfor various modes of stimulation.

In this embodiment, a recipient can be implanted with the device 50 andthe short array 51 can be inserted into the cochlea of the recipient toprovide hearing sensation for sounds having a high frequency. In thiscase, the conventional array 52 can be stored for future use, either bycoiling the array in the mastoid or packaged in a sack, made for examplefrom Teflon, remote from the cochlea. In this regard, should therecipient perceive that middle to low frequency sounds are no longerbeing experienced through the residual hearing process, then the shortarray 51 could be simply removed and the conventional array inserted,thereby restoring sound perception for all sound frequencies in the samemanner as a conventional cochlear implant device. In this embodiment,the device is easily upgraded to a conventional cochlear implant deviceshould the need arise without the need for extensive explantation andrevision surgery.

In yet another embodiment of the present invention, a thin electrodearray of the same length as conventional electrode arrays could beinserted into the cochlea, having a plurality of electrodes positionedalong the length thereof for applying stimulation to the surroundingregions of the cochlea. Such a thin array with reduced volume may bemade by the technique as discussed in the Applicant's co-pendingInternational Patent Application PCT/AU02/00272, the contents of whichis incorporated herein by reference. In this construction, theimplantable component may look quite similar to the component depictedin FIG. 6 but without electrode array 51. In this regard, the thinelectrode array is fully inserted into the cochlea, however, only thosemost basal electrodes are “switched on” to apply stimulation to thecochlea representative of high frequency sounds. In this situation, themore apical electrodes are not active and the recipient relies upon thenaturally present hair cells in the cochlea to receive and interpret thesounds. As the electrode array is of a small volume and a thincross-section, natural hearing is possible and the hydrodynamic natureof the cochlea is preserved. In this embodiment, as the recipient'shearing deteriorates over time and the ability to perceive the middle tolow frequency sounds deteriorates, the electrodes can be progressivelyactivated to provide electrical stimulation over time, without the needto remove the electrode array from the cochlea.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the invention as shown inthe specific embodiments without departing from the spirit or scope ofthe invention as broadly described. The present embodiments are,therefore, to be considered in all respects as illustrative and notrestrictive.

The invention claimed is:
 1. An implantable component of a cochlearimplant system, the implantable component comprising: a stimulator unitconfigured to output one or more stimulation signals; and first andsecond elongate electrode assemblies extending from the stimulator unitand positionable in a cochlea; wherein the stimulator unit is configuredto apply the stimulation signals via the first electrode assembly whenthe second electrode assembly is positioned external the cochlea and thefirst electrode assembly is positioned internal the cochlea, and whereinonly one of the first and the second elongate electrode assemblies ispositioned internal the cochlea at a one time, and wherein the secondelectrode assembly is stored in a removable biocompatible package whenpositioned external the cochlea.
 2. The implantable component of claim1, wherein the first elongate electrode assembly has fewer electrodesthan the second electrode assembly and is configured to apply thestimulation signals to the basilar region of the cochlea when insertedin the cochlea.
 3. The implantable component of claim 2, wherein thesecond electrode assembly is configured to apply the stimulation signalsto the basilar region of the cochlea and also to the region beyond thefirst basal turn when inserted in the cochlea.
 4. The implantablecomponent of claim 1, wherein the second electrode assembly isconfigured to apply the stimulation signals to the basilar region of thecochlea and also to the region beyond the first basal turn when insertedin the cochlea.
 5. The implantable component of claim 1, wherein thestimulator unit is configured to apply the stimulation signals via thesecond electrode assembly when the first electrode assembly ispositioned external the cochlea and the second electrode assembly ispositioned internal the cochlea.
 6. A cochlear implant systemcomprising: an implantable component comprising: a stimulator unitconfigured to output one or more stimulation signals; first and secondelongate electrode assemblies extending from the stimulator unit andpositionable in a cochlea; wherein the stimulator unit is configured toapply the stimulation signals via the first electrode assembly and notthe second electrode assembly when the second electrode assembly ispositioned external the cochlea and the first electrode assembly ispositioned internal the cochlea, and configured to apply the stimulationsignals via the second electrode assembly and not the first electrodeassembly when the first electrode assembly is positioned external thecochlea and the second electrode assembly is positioned internal thecochlea, and wherein only one of the first and the second elongateelectrode assemblies is positioned internal the cochlea at a one time,and wherein the second electrode assembly is stored in a removablebiocompatible package when positioned external the cochlea.
 7. Thesystem of claim 6, wherein the first elongate electrode assembly hasfewer electrodes than the second electrode assembly and is configured toapply stimulation to the basilar region of the cochlea when inserted inthe cochlea.
 8. The system of claim 7, wherein the second electrodeassembly is configured to apply the stimulation signals to the basilarregion of the cochlea and also to the region beyond the first basal turnwhen inserted in the cochlea.
 9. The system of claim 6, wherein thesecond electrode assembly is configured to apply the stimulation signalsto the basilar region of the cochlea and also to the region beyond thefirst basal turn when inserted in the cochlea.